Counterion effect on the spin-transition properties of the second generation iron(III) dendrimeric complexes

Abstract

The magnetic properties and the influence of counterions on the spin crossover properties of two novel Fe(III) dendrimeric complexes of the second generation, namely [Fe(L)2]+X-, where L = 3,5-di(3,4,5-tris(tetradecyloxy)benzoyloxy)benzoyl-4-oxy-salicylidene-N'-ethyl-N-ethylenediamine X = Cl- (1), ClO4- (2), have been studied for the first time by magnetic susceptibility measurements and electron paramagnetic resonance (EPR) method in a wide (4.2-300 K) temperature range. EPR results showed that compound 1 contains about 98% of high-spin (HS, S = 5/2) and 2% of low-spin (LS, S = 1/2) Fe(III) centers, and undergoes an antiferromagnetic ordering below 7 K. The EPR integrated intensity of a broad line (g 2), corresponding to the HS iron(III) centers, passes through a broad maximum at Tmax 100 K, which is indicative of short-range correlation effects. The anomalous broadening of this EPR line at low temperatures with the critical exponent = 1.5 upon approaching the long-range orderi